(a) Field of the Invention
The present invention relates to a thighbone shaft, and particularly to a thighbone shaft which has a pole and a bolt mounted on an inclined threaded hole in the pole and which is adapted for artificial joint or the similar.
(b) Description of the Prior Art
As disclosed in Taiwan Patent No. 89219012, a conventional artificial joint has a thighbone shaft, which is made of titanium alloy and plants into a user's thighbone. The thighbone shaft comprises:
a front portion, which shrinks gradually and is covered by an adhesion layer and a coating layer, a neck portion connecting with an end of the front portion, a sleeve portion connecting with the neck portion;
a middle portion connecting with an end of the front portion and opposite to the neck portion, and forming a rough surface;
a tail portion connecting with an end of the middle portion, and forming a polishing surface, symmetric grooves being defined in the polishing surface.
In this design, stress force put on the tail portion is reduced, thereby avoiding pain feel of thighbone side, achieving optimal planting effect, and decreasing occurrence of strain barrier. However, this design damages large area of thighbone and produces large area of wound. Moreover, the thighbone shaft is relatively large. The overall thighbone shaft has to be replaced when the thighbone shaft is worn out after long period of use. Such a thighbone shaft cannot meet users' need.